The present invention relates to methods and compositions for cementing applications. More particularly, the present invention relates to polyalkenoate cement compositions comprising soluble crosslinking agents, and methods of using such compositions in cementing applications.
Cements are commonly utilized in a number of different applications including structural (e.g., in the construction of buildings and roads), medical applications (e.g., dental and bone), and energy (e.g., subterranean well completion and remedial operations). The primary components of typical cement compositions include a hydraulic cement, water, rock, and sand. The undesirable attributes of these typical cement compositions include poor flexibility, low tensile strength, and the inability to effectively control hardening time.
Conventional polyalkenoate cement compositions generally include: water, a polyelectrolyte, and a partially soluble acid-degradable glass, which acts as both a crosslinking agent and a filler. The mechanism of crosslinking, and therefore hardening, in these compositions is dependent on the dissolution of the partially soluble acid-degradable glass. Thus, it is difficult to control the rate of hardening. In addition, large quantities of expensive acid-degradable glass often are required in these compositions. Supplementing with a non-soluble filler generally is not desirable as it would reduce the amount of active components in the composition.
In some applications, successful placement of a cement composition in a desired location requires controlling the setting time of the cement composition. However, to develop sufficient strength for an application, it is preferable for the setting time to be relatively quick. These competing factors must be balanced to provide a cement composition with sufficient mechanical properties, while also ensuring that the cement composition is able to be successfully placed in a desired location. Thus, the ability to control the setting characteristics of a cement composition is desirable. Moreover, the cement composition must have enhanced mechanical properties to sustain the stressful conditions that may be encountered in a particular application. For instance, the cement composition should develop high bond strength after setting and should also have sufficient mechanical properties, including but not limited to, elasticity, flexibility, compressibility, and ductility, to resist cracking and/or shattering as a result of any stressful conditions.
Hydraulic cement compositions are commonly utilized in construction and subterranean applications. Examples of common subterranean applications include, but are not limited to, subterranean well completion and remedial operations. For instance, hydraulic cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. To ensure that the annular space is completely filled, oftentimes a cement slurry is pumped into the annular space until it circulates to the surface. The cement composition is then permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement. The hardened cement substantially supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore. Hydraulic cement compositions are also used in remedial cementing operations, such as, plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.